Place the lentils in a deep bowl and cover with cold water. Leave to soak for 10–12 hours. Transfer to a colander and rinse under cold running water. Drain and place in a medium saucepan with the measured boiling water. Bring to the boil, then reduce the heat to low. Simmer gently for 35–40 minutes, skimming off any scum that rises to the surface and stirring often.
Meanwhile, heat the oil in a large saucepan and add the onion, garlic, ginger and chillies. Stir-fry for 5–6 minutes and then add the turmeric, paprika, cumin, ground coriander, kidney beans and lentils.
Add the measured water and bring to the boil. Reduce the heat and stir in the spinach. Cook gently for 10–15 minutes, stirring often. Remove from the heat and season to taste. Stir in the chopped coriander and drizzle over the yogurt. Sprinkle with a little paprika and serve immediately with parathas.